1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a control sub-unit and control main unit that are suitable for constructing an integrated system for a vehicle.
2. Background Art
A known vehicle control system disclosed by JP-A-2004-136816 includes a main unit and a plurality of sub-units that are subordinate to the main unit. When this system configuration is employed, the main unit can use the sub-units to efficiently detect abnormalities. This system configuration also makes it possible to reduce the amount of communication data. The above-mentioned vehicle control system achieves the purpose of the main unit by allowing the plurality of sub-units to execute instructions from the main unit. To achieve the purpose of the main unit, the main unit determines instructions that are to be issued to the sub-units. In this instance, the instructions issued by the main unit could be unpredictable by the sub-units. Other prior art includes JP-A-2004-249980, JP-A-2002-67833, JP-A-2003-191774, JP-A-2005-199951, JP-A-1992-238745, and JP-A-1992-131561.
In the conventional vehicle control system described above, the main unit recognizes an abnormality deviating from an ideal state after it occurs in a sub-unit. In other words, the system including the main unit and sub-units is not capable of inhibiting the sub-units from becoming abnormal. The above abnormality may occur when, for instance, a sub-unit executes an instruction issued by the main unit in the above-mentioned ideal state without considering whether the instruction is executable. When all instructions issued by the main unit are indiscriminatingly executed in the above-mentioned conventional system, an abnormality occurs, causing the sub-units to deviate from their ideal state.
When an abnormality in a sub-unit is recognized, a vehicle control system having a main unit and sub-units generally shuts off the power supply to the sub-unit. Shutting off the power supply achieves a vehicle control purpose of bringing a vehicle to a safe stop. However, no output is generated from the sub-unit that is turned off. Eventually, the system cannot produce a desired output.